Fire tube boiler or water heater



July 16, 1968 J. J. WOLFERSPERGER 3,392,711

FIRE TUBE BOILER OR WATER HEATER Filed Dec. 9, 1966 2 Sheets-Sheet 1 0) W k k k I @0099 I! woeag I 'a'w jc z 6 99960 5 D99 i @909 i 1 009999699 1 g I @wom 5 -i l T l 1 i I 2* Q I q "3 I I z i if! i i i S i (E M i i \3 i 3 I s I I //v VEA/ TO}? K JOHN J. WOL FERSPERGER BY 0%, CI/MWLA ATTORNEYS July 16, 1968 J. J WOLFERSPERGER 3,392,711

FIRE TUBE BOILER OR WATER HEATER Filed Dec. 0, 1966 In N k 2 Sheets-Sheet 2 I IV VE/V 70/"? JOHN J. WOLFE RSPE R65 R 4 T TORIVEYS United States Patent r 3,392,711 FIRE TUBE BOILER 0R WATER HEATER John J. Wolfersperger, 21 Strawberry Circle,

Mill Valley, Calif. 94941 Filed Dec. 9, 1966, Ser. No. 600,613 7 Claims. (Cl. 122-52) ABSTRACT OF THE DISCLOSURE A Water heating device having a plurality of parallel short tubes extending in a straight line between two tube sheets, combined with a fuel burner that completely burns the fuel and exhausts the burned mixture into the tubes at a velocity higher than that at which stratification ends and turbulence begins. Ratings of more than 500% are attainable within a small space. Bare metal surfaces need no refractory coating. A calculation procedure for sizes and number of tubes is given.

This inveniton relates to an improved fire tube boiler and to an improved boiler-burner combination.

Heretofore, boilers have had large-diameter fire tubes that were so long that they had to be divided at intervals into a plurality of runs or passes, generally at least two passes and often three or four, in order for the length of the boiler to be reasonable. This has added to the expense of boiler manufacture and has made boilers excessively heavy.

In contrast, my new boiler uses shorter and smallerdiameter tubing and makes it practical to design all capacities, large and small, with the burner, combustion chamber, and tubing in the same straight line and in a single pass-all without excessive boiler length and without excessive weight. In fact, the entire unit is shorter than most conventional tw-o-, threeand four-pass boilers of the same capacity.

An important object of my invention is to provide a boiler having a very high rating. Boiler rating equals the horsepower obtained from each 10 square feet of heating surface. A boiler rating of 100% means that the boiler produces one horsepower of heat energy per 10 square feet of heating surface. Thus, when one horsepower is obtained from five square feet of surface, the boiler is given a 200% rating, which is about the highest rating obtained by conventional boilers. I know of no conventional boilers that have operated as high as 500%, which means two square feet of heating surface per horsepower. However, by using the present invention, boilers become practical at not only a 500% rating but at much higher ratings.

The boiler of this invention obtains a very concentrated use of metal for heat transfer by means of smalldiameter fire tubes and by causing a high velocity of flow of combustion products through the tubes. The use of smaller diameter tubing with higher velocity of flow greatly increases the turbulence of the flow, and the greater turbulence causes increased contact of the hot gas molecules with the metal heating surfaces of the boiler plate and tubing.

I am able to dispense with all the refractory material which heretofore has beenused in burners and combustion space, because the burner metal is air-cooled and the combustion of gas and of prepared burner oils is completed so quickly that only the products of complete combustion come in contact with any water-jacketed surface of the combustion chamber or tube sheet or tubing. Refractory coatings may be used, if desired.

The boiler of this invention is designedfor use with burners of a type which attain complete combustion before the fire tubes are reached. The only examples I know of such burners are those in my own Patents 2,499,207, 3,266,549, and 3,276,693. These burners reduce the combustion space drastically and obtain complete combustion in a very short distance and within a very small space compared to that required by conventional burners.

The boiler can be used to generate steam or hot water or to heat any other liquid. By omission of the burner, the boiler unit itself can be used as a waste-heat boiler, which is much smaller and lighter in weight than conventional waste-heat boilers. For example, the inlet end of the boiler combustion chamber can be attached to the exhaust outlet of an oil refinery retort of the type that uses products of combustion only when they are above the chosen value, say 1000 F. or 1300 F., and discards them when they are cooler than that. The flow of the waste heat through the boiler may be accomplished by increasing'the pressure of the hot gases through the re tort or by using an exhaust fan on the boilers exhaust end.

One important feature of the invention is that the smaller the tube diameter, the smaller the volume of hot gases in the tube at one time, so that all gas molecules are closer to the inner surface of the tube. This means that the gas molecules make contact with the tube surface more frequently as they flow through the tube; hence, the smaller volume of gases is cooled to the desired exhaust temperature in a much shorter distance than is possible in larger diameter tubes. That is why the tube length can be shorter.

Using smaller diameter tubes means that there must be a greater number of tubes; this involves the boring of more holes, but smaller holes, in the tube sheet and the expanding or welding of more but smaller tube ends into the tube sheet. Even if additional cost were involved, this would be more than worthwhile, because of the higher rate of heat transfer per unit of surface and because the short-er tubes mean that a shorter boiler shell can be employed, so that there is a lighter weight for the entire assembly. The structure also enables single-pass construction for all capacities, so that there is generally a smaller initial cost of manufacture than for the conventional boilers, rather than an increase in cost.

Just as important to the increase of heat transfer per unit of surface is the high velocity of flow of the hot gases through the tubes. In larger diameter tubing, the gas flowing through the tubes is stratified, until or unless the velocity of the flow exceeds what is termed a critical velocity, i.e., the velocity at which stratification breaks up and turbulence begins. Data on critical velocity seem to be scarce but from what I have found in textbooks emanating from experts, indications are that critical velocity, in tubing ranging from 2 /2 to 3 /2 O.D., ranges from about 200' to 300' per second at the inlet end of the tubing. My own experience in raising the ratings in conversion jobs verifies the above approximations. For a conventional twenty to twenty-five horsepower boiler operating at rating with three-inch diameter tubing, the flow of gases is s'tratified and the velocity lies well below the critical velocity; therefore, heat transfer is slow, since the hot gas molecules seldom contact the actual tubing surface, due to the Stratification.

However, I have found that if the three-inch tube bank is replaced with a tube bank of half-inch tubing of a sutlicient number of tubes to give a velocity of flow the same as through the three-inch tubing, the heat transfer is increased several-fold, because all the gas molecules in the half-inch tubing lie closer to the tribe surface, and the velocity of flow in the half-inch tubing is turbulent because the critical velocity for this small size of tubing is lower than the actual velocity. Hence, the smaller the diameter of the tubing, the lower the critical velocity. In my invention, by selecting smaller-size tubing, the velocity of flow is always above the critical velocity, because after the critical velocity is attained, heat transfer increases proportionally, or nearly proportionally, to the increase in rating. For example, the flue gas temperature at 500% rating is the same or only negligibly higher than at 300% or 400% rating, when using tubing with higher-than-critical velocity at these ratings. Thus, the velocity of flow, the heat transfer, and the rating all move in practically a direct proportion. Much improvement results through using my smaller diameter tubing.

As a result of the increase in heat transfer per square foot of heating surface and of the use of straight tubing, the cost per horsepower of manufacture, handling, and installing the small lightweight boilers of this invention is much less than the cost for conventional boilers of the same capacity, in addition to the saving due to less fioor space being required for this small boiler.

In my invention, the total internal volume of the burner, combustion chamber, and tubing is so small that any delayed ignition of an explosive mixture is harmless, because only stout steel construction is used, and no refractory material is present to be damaged. Also, there are no large-volume chambers for gas to accumulate in, as are required for conducting gases from one pass to the next pass in conventional multipass boilers.

Other objects and advantages of the invention will appear from the following detailed description of a preferred embodiment.

In the drawings:

FIG. 1 is a view in elevation and partly in section of a steam boiler embodying the principles of the invention.

FIG. 2 is an end elevation view looking from the left of FIG. 1.

FIG. 3 is a view in section taken along the line 3-3 in FIG. 1.

FIG. 4 is a view similar to FIG. 1 of a water heater embodying the principles of the invention.

In the embodiment shown, my new boiler is associated with a burner unit 11, which is preferably that shown in either of my US. Patents Nos. 3,266,549 and 3,276,693. The burner unit 11 is attached to an inner flange 12 at the inlet end of a combustion chamber 14 and leads directly by a frustoconical outlet 13 into the cylindrical combustion chamber 14, which is inside the boiler 10. As explained in the above patents, substantially complete combustion of gas and of suitable burner oils is obtained, and the gases are completely burned by the time they reach a tube sheet 15 at the far end of the combustion chamber 14; hence bare metal surfaces are usually preferred to those covered with refractory material. In lieu of the burner 11, which has been mentioned, the boiler 10 may be used in connection with any unit supplying completely combusted high-temperature gases, such as the waste gases in oil refineries.

The boiler 10 has end walls 16 and 17 and a cylindrical wall 18 with a feed-water inlet 20 and a steam outlet 21, defining the water and steam space 22. The rear end-wall 17 is also the rear tube-sheet, in and through which are attached the outlet ends of tubes 23 whose inlet ends are attached to the forward tube-sheet 15. The outlet ends of the tubes 2'3 discharge the exhaust gases into a circular exhaust chamber 24, the chamber 24 being welded to the outiside face of the rear-plate-and-tube-sheet 17, surrounding the tube-bank. The exhaust chamber 24 has a collar 25 around a hole 26 at the top for attaching a vertical vent pipe (not shown), and the rear of the chamber 24 is closed by an end-plate 27 bolted to an outside circular flange 28. This removable end-plate 27, which gives easy access to the tubes 23, may have a sight glass 29.

The rear end wall 16 may be provided with a clean-out hole 30, normally closed by a plug 31. Inside the boiler 10, it is normal to keep a water level 32 a couple of inches above the combustion chamber 14. Water 33 lies below the level 32 and there is a steam space 34 above this level. There may be a drain 35 and a safety valve 36.

The water heater 40 shown in FIG. 4 is generally similar, except that there is no steam space 34, so that the heater 40 is of smaller diameter. By way of example only, the burner .11 of FIGS. 1-3 is shown as a gas-burner, and a burner 41 is shown in FIG. 4 as an oil burner; however, they could be interchanged, of course. As a result of the smaller diameter of the heater 40, the front end wall 45 and the rear end wall 44 have narrower diameters, but most of the other parts (e.g., the front tube sheet and combustion chamber) are the same as in the boiler 10. Again, the bundle of tubes 42 (like the bundle of tubes 23) is axially in line with the burner and combustion chamber. A thermometer 46, aquastat 47, and relief valve 48 are shown.

The diameter of the tubes 23 and 42 is at least small enough such that the forced flow rate of gas from the chamber 14 to the chamber 24 through the tubes 23 lies above the critical velocity, as discussed above. All of the tubes 23 and 42 are in heat exchange relationship with the liquid in the boiler water space 33 or in the water heater 40, and all extend in a single path through it to the tube sheet 17 or 44. At this tube sheet 17 or 44 the gases, which have been substantially cooled due to the cooling power of the water in the boiler, are exhausted into the collection chamber 24 and from there are sent by a vent pipe (not shown) attached to the collar 25 into the outer atmosphere.

My invention provides a simple method of calculating tube-banks for boilers, because my use of small diameter tubing makes it practical to design all capacities singlepass; and further because my small, short combustion space requirement, and my high velocity of flow through that space, of very concentrated and stoutly Stratified flame and gas, hold heat transfer in my combustion chamber down to a negligible amount, so that the heating surface of my combustion chamber walls can be omitted from my tube-bank computations. Experimental results confirm that the omitted heat transfer is negligible. (The combustion chamber heat transfer is so low because practically no hot gases contact the walls to be convected through to the boiler water, and the flame is so narrowly concentrated and the area of its exposed surface so small that radiation to the combustion chamber walls is negligible.)

The calculation procedure is as follows: A unit value of internal cross-sectional area of tubing per horsepower for a chosen rating is obtained from data on any particular burner-boiler unit of mine that has been in operation, on which are known the fuel input, the size and number and gauge of the tubing, and the rating, and that it has a satisfactory flue gas temperature. Then the sum-total internal cross-secti0nal area of all the tubes of this boiler is divided by the boilers horsepower to give the value of cross-sectional area per horsepower for this particular rating.

This unit value is multiplied by the horsepower chosen for any other job of the same rating to be calculated, thereby giving the total internal cross-sectional area of the tubing for this job. The internal cross-sectional area of a single tube of the tubing chosen for this job is divided into the total internal cross-sectional area to give the number of tubes required.

Next, the total square footage of surface required is calculated by multiplying the chosen horsepower by the square-foot per horsepower of the chosen rating. This product, the total square footage of surface, is divided by the outside surface, in square feet, of one linear foot of the chosen tubing, gives the total footage of tubing required. Dividing this total footage of tubing by the number of tubes, as derived above, gives the length of each tube and completes the computation.

From laboratory test boilers operating at 500% rating I have found that it requires about 0.459 square inch of internal cross-sectional area of tubing for the generation ol one horsepower. Assuming, for example, a sixty horsepower burner-boiler combination operating at 500% rating, the total internal cross-sectional area of the tube bank would be 60 x .459 square inch or 21.54 square inches.

Characteristics of tubing diameters are that the larger the tubing diameter the longer the tubing has to be; and the smaller the tubing diameter the shorter the tubing, to produce the desired low temperature flue gas. Assuming the same sixty horsepower unit, keeping these characteristics in mind, we select Ad -12 gauge tubing as an example. (The tubing selected should be of small enough diameter to have a velocity of flow above critical velocity at 500% rating, as a A -IZ gauge tube has.) The internal cross-sectional area of a /1"12 gauge tube is 0.2223 square inch so that the above 27.54 square inches divided by 0.2223 gives the number of tubes required for the tube-bank, or 123 tubes in this example.

One linear foot of tubing has 0.1964 square foot (easily. calculated or obtainable from engineering handbooks) of outside surface, and as 2 square feet of surface per horsepower are required for operating at 500% rating, the total required surface is .60 x 2 or 120 square feet. Dividing 120 square feet by .1964 square feet gives the total footage of tubing required, or 611 feet; and dividing 611 feet by the previously determined 123 tubes gives the length of each tube of the tube-bank, or 4.96 or about 5 feet, which completes the data needed for the design of the tube-bank. This tube length is about 1% times the approximately 3-footshell diameter 'of a 60 horsepower boiler, which ratio comes within my preference as to the shape of the boiler. (16 gauge and 12 gauge tubing assume 100 pounds to 150 pounds steam pressure. If steam pressure is to be higher and to require a thicker gauge, then select a heavier gauge or a larger diameter tubing: of adequate gauge and recalculate as per above.)

The foregoing method of procedure for tube bank For each rating below, this table gives the internal cross-sectional area of tubing per horsepower and the external surface of tubing per horsepower.

The design of this single-passboiler is very flexible and is adaptable to wide variations in floor space, i.e., longer and narrower, or shorter and wider floor space. In absence of other specifications, my preference is more or less midway between extremes. For steam boilers I prefer to have the length of the tube-bank approximately equal to twice the diameter of the boilers shell, with tube length limits not less than 1 /2 nor more than 2 /2 times shell diameter.

As to rating, while adaptable to higher and lower ratings, it should be noted that 500% rating is high enough to be an improvement on the 200% limit currently of conventional boilers, and low enough not to require excessive air pressures. The same flexible design characteristics and rating comments apply also to water heaters, but due to the elimination of steam space, the shell diameter would be reduced by about /3, so that the tube-bank length would be approximately 3 times the water heater shell diameter, with low limit of 2 /2 and high limit 3% times the water heater shell diameter.

The following tabulation illustrates the above preference in steam boilers designed to operate at 500% rating:

TABLE II Number Length Approximate Tube Lengths Boiler, Tubing, Tubing of of I Shell as Multiple of HP O.D., in. Gauge Tubes Tubes Diameter, in. Approx. Shell Diameter design is adaptable not only to 500% rating units but to all other ratings from 100% to 1000% and up. (After 1000% rating much greater air power is required as compared with conventional standards.)

Of the several factors used in this procedure, only two need to be given different values in order to be adaptable to calculations of the designs of any rating. For every different rating there is a different internal cross-sectional area of tubing required for the generation of one horsepower. With this determined in the laboratory from a boiler operating at any specific rating, all other internal cross-sectional areas can be calculated for all ratings. The second item that is different for every different rating is the unit amount of heating-surface per horsepower. Knowing that 2 square feet per horsepower is 500% rating or that 10 square feet is 100% rating, it is a. very simple matter to calculate the units of heating-surface for all other ratings.

Velocity of flow of completed-combustion products in inlet end of tube-bank The following velocity of flow figures are derived from computations involving quantity of fuel, volume of air and temperature in combustion chamber.

TABLE III At 100% rating87 per second Same velocity of How for all boiler capacities at this rating. At 200% rating-174 per second Do.

At 1,000% rating-870 per second.

TABLE IV.LENGTII OF BOILER COMBUSTION lIAM- BERS FOR BURNERS OF DIFFERENT CAPACITIES To those skilled in the art to which this invention relates, many changes in construction and widely diflering embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. A water-heating device, including in combination,

a generally cylindrical housing with end walls and water inlet and outlet means,

a tube sheet in said housing having a plurality of parallel tubes extending in a straight line between an inlet tube plate in said housing and an outlet tube plate in said housing, and

fuel-burning means in said housing for burning a combustible mixture completely and for continuously exhausting the burned mixture to said inlet tube plate and into said tubes at a velocity through said tubes above the critical velocity at which stratification breaks up and turbulence begins.

2. The device of claim 1 wherein said fuel-burning means includes a cylindrical burner and a cylindrical combustion chamber directly in line with said tubes and cooperating with them and said tube sheets to define a barrier to the water inside said housing.

3. The device of claim 2 wherein said burner and said combustion chamber have bare metal surfaces.

4. The device of claim 1 as a boiler wherein there is means for maintaining water at a level in said housing above said combustion chamber with steam thereabove, said tubes being below water level.

5. The device of claim 1 as a hot-water heater wherein said housing is filled with water and is concentric with said burner and tubes.

6. A water heating device, including in combination:

a generally cylindrical housing with end walls and water inlet and outlet means,

manifold means in said housing separated from the water therein,

means for burning a combustible mixture substantially completely and for introducing the burned mixture to said manifold means generally parallel to the axis of said housing at a known high velocity,

a plurality of tubes in said housing leading from said manifold means to exhaust means in a single straight pass, each tube having a diameter suchthat passage of said burned mixture through said tube is at a velocity above that at which stratification breaks up, so that there is turbulence.

said tubes being numerous enough so that the total internal cross-sectional area is sufficient for a desired horsepower at a desired rating,

said tubes extending straight in the axial direction of said housing, each tube being spaced from the others and its outer surface in contact with the water, the length of all said tubes being substantially identical and sufiicient to give a total external tube surface sufficient for obtaining said desired horsepower.

7. The device of claim 6 wherein the internal surfaces of said housing, manifold means, and means for burning are bare metal.

References Cited UNITED STATES PATENTS 1,974,177 9/1934 Doucha 12224 2,581,316 1/1952 Wolfersperger 122-134 2,715,390 8/1955 Tenney et a1. 122 -24 KENNETH W. SPRAGUE, Primary Examiner. 

